1. Technical Field
The present disclosure relates to boilers and, more particularly, to efficient boilers configured to heat a receiver medium, e.g., water, from an approximately room temperature liquid to a hot liquid, vapor, and/or superheated vapor (depending on the particular purpose). The present disclosure also relates to systems incorporating such boilers, e.g., stove systems, home heating systems, power generating systems, etc.
2. Background of Related Art
In conventional boilers, a source medium, e.g., a hot gaseous fume, is utilized to heat a receiver medium, e.g., water, via heat exchange through a thermally conductive exchange material disposed therebetween. However, resistance in such conventional boilers results in much of the heat energy escaping as waste, severely reducing the efficiency of these boilers.
Whether boiling a pot of water using a gas stove, using an oil burner to generate water vapor for a home heating system, generating superheated water vapor for a steam turbine, or utilizing any other conventional boiler system, resistance in the heat exchange process results from the formation of a thin layer of molecules on the surface of the exchange material, e.g., the thermally conductive material disposed between the source medium and the receiver medium, and serves to hamper heat exchange therebetween. In particular, according to boundary layer theory, in such conventional boilers, molecules from the source medium become stuck to the surface of the exchange material because of friction and eventually attain the same temperature as the exchange material, forming a so-called boundary layer. This boundary layer inhibits the exchange of heat from the source medium to the receiver medium through the exchange material, and is referred to as boundary layer resistance.
To reduce boundary layer resistance, the rate or speed at which the source medium is circulated through the boiler has to be increased for momentum exchange between the boundary molecules and the main stream molecules of the source medium to occur. As the speed increases, a turbulent flow pattern results with some of the colder boundary molecules being displaced by the hotter main stream molecules. This is referred to as forced convection, and results in enhanced heat exchange.
However, increasing the speed of the source medium is not without shortcomings. In particular, the source medium must be confined within the boiler for a sufficient amount of time to allow the receiver medium to absorb enough energy to be sufficiently heated to the desired temperature, e.g., a hot liquid, vapor, or superheated vapor. Unfortunately, confinement of the source medium within the boiler is not easily achieved because the source medium has a tendency to escape and the hotter the source medium, the faster it escapes. In other words, the constraint on efficiency of a boiler is that in a limited time interval, quick and effective heat exchange is required.
Regardless of how turbulent the source medium becomes, it cannot deliver enough energy for the receiver medium to absorb to sufficiently heat the receiver medium before the source medium escapes through the chimney. This is because of an impedance mismatch between the source medium and the receiver medium that exists in conventional boilers. This impedance mismatch in conventional boilers stems from the fact that the energy densities (BTU/ft3) of the source medium (typically a gaseous fume) is several orders of magnitude less than that of the receiver medium (typically liquid water), due to the different thermodynamic parameters, e.g., density (lb/ft3), specific heat (BTU/lb×° F.), and conductivity (BTI/hr.-ft ° F.), of the source medium and the receiver medium. Such a severe impedance mismatch between the energy provider, i.e., the source medium, and the energy receiver, i.e., the receiver medium, renders the source medium unable to adequately transfer heat to the receiver medium and, as a result, conventional boilers are inefficient.